There's nothing particular special required. There's no real "modding" involved, this is simply a Photoshop edit, no different than if you touched up a photo. You need to paint out the beard to make it look like bare skin. Google "photoshop remove beard" and you should get a zillion tutorials that cover all the basic principles.
You can also check out the original source textures that the mod is based on. You might be able to merge them together if the beard was added in.